Electron transfer in complex I from Escherichia coli was investigated by an ultrafast freeze-quench approach. The reaction of complex I with NADH was stopped in the time domain from 90 mus to 8 ms and analyzed by electron paramagnetic resonance (EPR) spectroscopy at low temperatures. The data show that after binding of the first molecule of NADH, two electrons move via the FMN cofactor to the i...

The electroreduction of COT in liquid ammonia at -38° and -65°C was investigated by cyclic voltammetric and controlled potential coulometric techniques. The results are interpreted by a two-step two-electron transfer reaction with strong ion-pairing of the COT dianion. Values for the heterogeneous electron transfer rate constants and the equilibrium constant of the disproportionation of the rad...

Introduction Most of the recent intense scientific effort towards providing an understanding of electron transfer in proteins has focused on intraprotein electron transfer and on the pathway between the donor (D) and acceptor (A) redox centres. These centres are usually fixed within the protein matrix as in the case of the photosynthetic reaction centre [ l ] , or involve attaching an artificia...

The study of photoinitiated electron transfer in donor-bridge-acceptor molecules has helped elucidate the distance dependence of electron transfer rates and behavior of various electron transfer mechanisms. In all reported cases, the energies of the bridge electronic states involved in the electron transfer change dramatically as the length of the bridge is varied. We report here, in contrast, ...

Photosynthetic water oxidation by photosystem II is mediated by a Mn4 cluster, a cofactor X still chemically ill-defined, and a tyrosine, YZ (D1-Tyr161). Before the final reaction with water proceeds to yield O2 (transition S4-->S0), two oxidizing equivalents are stored on Mn4 (S0-->S1-->S2), a third on X (S2-->S3), and a forth on YZ(S3-->S4). It has been proposed that YZ functions as a pure el...

The primary electron transfer has been investigated by femtosecond time-resolved absorption spectroscopy in two chemically modified reaction centers (RC) of Rhodobacter sphaeroides, in which the monomeric bacteriochlorophylls BA and BB have both been exchanged by 13(2)-hydroxybacteriochlorophyll a or [3-vinyl]-13(2)-hydroxybacteriochlorophyll a. The kinetics of the primary electron transfer are...

A homologous series of DNA-modified electrodes has been investigated in which the molecular tether length varies. Using intercalated, covalently bound daunomycin as a redox probe, an exponential dependence of electron transfer rates on the number of intervening methylene groups in the sigma-bonded tether is observed. In contrast, variation in DM position within DNA yields no detectable change i...

Absolute rate constants for the reaction of NADH with thiyl free radicals derived from various sulphur-containing compounds of biological significance were measured by using the technique of pulse radiolysis. These and related reactions with phenoxyl free radicals are believed to occur through one-electron-transfer processes. Further evidence comes from studies with deuterated NADH. The results...

The synthesis of a series of donor–acceptor podands is described. The dependence of the rate constants of intramolecular photoinduced electron transfer on the exothermicity of the reaction was studied by stationary and time-resolved fluorescence spectroscopy. H NMR and computational studies suggest that the conformational change of the podands is restricted by K binding. As a result, the occurr...

This report describes the thermochemistry, proton-coupled electron transfer (PCET) reactions and self-exchange rate constants for a set of bis-benzimidazolate-ligated [2Fe-2S] clusters. These clusters serve as a model for the chemistry of biological Rieske and mitoNEET clusters. PCET from [Fe2S2((Pr)bbim)((Pr)bbimH)](2-) (4) and [Fe2S2((Pr)bbim)((Pr)bbimH2)](1-) (5) to TEMPO occurs via concerte...